The present invention relates to the temperature testing of electronic components and, primarily, the testing of electronic quartz resonators, whose electrical parameters are temperature dependent. For testing, a batch of resonators is mounted in a temperature chamber and heated or cooled to a specific temperature. When the resonator response has settled, it is measured. The process is repeated at other predetermined temperatures. For the measurement a test instrument is switched sequentially to each resonator by either electrical or mechanical means.
FIGS. 1 and 2 give an example of prior art according to Reference 1. They show a plurality of components 1 supported on a flat test ring 3. Leads of each component are inserted in sockets 5 and 7. The sockets are connected with a first series of electrical contacts 9 on one side of the test ring and with a second series of electrical contacts 9 on the opposite face of the ring. The test ring is mounted in a chamber 15 on a turntable means 17 which is linked via shaft 19 to a step motor 21 outside the chamber. An electrical connection assembly includes a pair of wiper springs 23 that, upon stepwise rotation, can connect the component leads to an adapter network 25 (such as shown in FIG. 4) connected to a measurement instrument 27 outside the chamber.
A source of coolant 29 controlled by a valve 31 releases coolant, which is circulated by a fan 33 through a vertical, central inlet bore to the temperature chamber 15. A baffle 39 has an upper horizontal edge which directs the coolant through central apertures in the turntable 17 and test ring 3 and over the top of the ring, cooling the components before returning to fan 33. For temperatures higher than ambient, a heater 35 is used to heat the circulating air and thereby the components. The temperature is sensed by sensor 37.
The motor 21 indexes the series of electrical contacts 9, 11 associated with each of the components 1 into electrical contact with wiper springs. The contact springs are connected via adapter network 25 with test instrument 27.
Another disadvantage is a limited temperature uniformity. A paramount requirement for temperature test systems is temperature uniformity for all components, i.e. at all component locations. In this regard, the described system has an inherent limitation because the airflow generated by fan 33 is not concentric (symmetric) with test ring 1.
To overcome this problem, another prior-art system according to Reference 2 is claimed to have symmetric airflow. It is shown schematically in FIG. 3, including a temperature chamber 39, a cylindrical xe2x80x9ctest wheelxe2x80x9d 41, and a xe2x80x9cchamber basexe2x80x9d 43 including xe2x80x9cheater, coolant, fan, and insulationxe2x80x9d, providing an airflow indicated by arrows 45.
Both described systems require, in addition to the temperature chamber, housing for the generation, conditioning, and guidance of the circulating airflow. This means xe2x80x9cwastedxe2x80x9d space, energy, and time for heating and cooling the additional volume and apparatus.
Another disadvantage of both systems is limited measurement accuracy. This is explained by reference to FIG. 4, in which a test instrument 51 is connected to a resonator 53 via an xe2x80x9cadapter networkxe2x80x9d 55 that includes several resistances and a xe2x80x9cload capacitancexe2x80x9d 57. High measurement accuracy requires that the length of the connection between resonator and adapter network be as short as possible. In both of the prior-art systems discussed above, this connection includes wiper contacts and wiper-terminals that connect to the resonator sockets. In contrast, the circuit according to the invention provides a direct, short (approximately 3 mm) connection from the adapter networks to the resonator terminals.
A further disadvantage of both described systems is the relative complexity of the thermal insulation, which has to conform to the outside of the cylindrical part of the chamber as well as to the rectangular housing for fan and heater, as shown in FIG. 1
The approach can be summarized by referring to FIGS. 5 and 7. FIG. 5 shows a cross section of a system according to the invention. FIGS. 7a and 7b is a cross section and top view, respectively, of a section of the system of FIG. 5. In both figures, a stepwise rotatable test ring 2 in a temperature chamber 4 includes guide holes 36 and electronic components 32 with terminals 34. It can be rotated by a step motor 20 via a pin wheel 22 with drive pins 24 that engage in guide holes 36. A vertically mobile contact head 26 includes guide pins 28 and contact pins 42. It can be moved up and down by a pneumatic solenoid 30. Each time the ring is rotated a step, the contact head moves down to first engage guide pins 28 with the guide holes 36xe2x80x94thereby accurately aligning the contact pins 42 with the terminals 34xe2x80x94and, upon further down movement, connecting the contact pins 42 with the terminals 34. Electrical measurements are made by a test instrument (not shown) that is connected to contact pins 42 via an adapter network 40. A centrifugal-fan wheel 8 is driven by a motor 10 and mounted concentric with test ring 2 so that the fan""s radially expelled air, indicated by arrows 12, flows across the ring, in parallel with the test ring surfaces. Air guides 14 guide the airflow over the test ring and heating/cooling elements 16 back to fan inlet 18.
This approach overcomes the disadvantages of prior-art systems and provides:
1. low chamber volume and thermal mass, achieved by locating the test ring so it is concentrically surrounding the centrifugal fan.
2. high temperature uniformity in the temperature chamber, achieved by providing symmetric airflow in the chamber.
3. high accuracy for electrical measurement of the components, achieved by a short, direct connection between component and an adapter network.
4. precise alignment of the component""s terminals with the contact pins, achieved by a re-alignment during each step of the test ring. High precision is essential because the dimensions of the component""s terminals may be smaller than 0.5xc3x970.5 mm.
5. high reliability and low cost, achieved by the simplicity of the design.
6. high thermal efficiency and simple application of thermal insulation, based on enclosing the systemxe2x80x94including heater and fanxe2x80x94in one cylindrical housing.